The present invention relates to vacuum-generating devices comprising at least one vacuum pump associated with a suction pipe and with a delivery pipe.
One of the frequent uses of a vacuum pump is to generate a vacuum in an enclosure for treating semiconductors.
During such treatment, materials are deposited on a semiconductor wafer. The efficiency of the deposition is relatively low, and the vacuum pump sucks up a large portion of the materials for deposition on the semiconductor. When the vacuum pump delivers at atmospheric pressure or at relatively high pressures, the pumped gases tend to condense and to solidify when their temperature is too low, which can degrade the effectiveness of the pump.
That phenomenon takes place essentially at the outlets of the primary pumps, where the pressure is high and where the gases cool rapidly as they leave the body of the pump.
That problem also occurs in the suction pipes, upstream from the pump, but to a lesser extent.
To limit such unwanted deposition, current solutions consist essentially in heating the pipes so as to prevent cold spots, which are the preferred places at which the gases condense and solidify.
Those solutions require additional energy to be supplied, and their effectiveness varies as a function of the gases being pumped and of the vacuum conditions.
The problem that the present invention proposes to address is to design new means making it possible for pumped gases to be prevented effectively from condensing and solidifying in the high-pressure zones of vacuum pumps, without requiring an additional external supply of energy to heat the pipes.
Another object of the invention is to design such means that make it possible simultaneously to reduce the noise given off by the vacuum-generating device, by preventing soundwaves from propagating.
The invention results from the observation that merely by insulating a vacuum pump pipe highly effectively by means of a vacuum layer interposed between the pipe and the ambient atmosphere, it is possible to maintain the pipe at a suitable temperature, thereby avoiding any risk of the pumped gases condensing or solidifying. In addition, the vacuum layer simultaneously provides effective sound insulation that blocks the outward propagation of soundwaves.
Thus, to achieve these objects and others, a vacuum-generating device of the invention comprises at least one vacuum pump associated with a suction pipe and with a delivery pipe, at least a portion of the vacuum-generating device being separated from the outside atmosphere by a volume in which a suitable vacuum prevails.
In a first embodiment, said volume in which a suitable vacuum prevails is gastight, thereby maintaining said suitable vacuum permanently.
In another embodiment, said volume in which a suitable vacuum prevails is connected to an external vacuum source which sustains said suitable vacuum.
In which case, advantageously, it is possible to make use of the fact that the invention is applied to a vacuum-generating device: the vacuum-generating device itself is then used as the external vacuum source.
In practice, to create said volume in which a suitable vacuum prevails, it is possible to provide a gastight double wall made up of two walls separated from each other, and said volume occupies the space between the two walls of the gastight double wall.
Alternatively, it is possible to provide a single wall around the vacuum-generating device; in which case, said volume in which a suitable vacuum prevails occupies the space between the gastight outer wall and a portion of the vacuum-generating device.
In a first application, said volume in which a suitable vacuum prevails is formed around the delivery pipe of a primary vacuum pump, so as to prevent the pumped gases from condensing and solidifying, and so as to reduce the noise given off.
In another application, said volume in which a suitable vacuum prevails surrounds internal devices for acoustically damping pulsating pressure and soundwaves (silencers, sound traps, etc.)
In another application, said volume in which a suitable vacuum prevails is formed around an intermediate or suction pipe element in the vacuum-generating device. It is thus possible to prevent the pumped gases from condensing and solidifying in the zones in which there is a risk of that occurring.
In another application, said volume in which a suitable vacuum prevails surrounds the vacuum pump itself. This use makes it possible to limit the noise given off by the pump.